Multistage hydrocarbon reforming process



2,866,745 Patented Dec. 30, 1958 Heinz l-Ieinemaiin, Swarthmore, Pa., assignor to Houdry Process Corporation, Wilmington, Del., a corporation of Delaware No Drawing. Application December 15, 1951 Serial No. 261,920

3 Claims. (Ci. 20879) This invention relates to improvements in catalytic reforming of hydrocarbon distillates boiling approximately in the gasoline range and is particularly concerned Wlill the dehydrogenation, dehydroisomerization and isomerization of naphthene ring hydrocarbons and hydrocarbon fractions containing the same to form products of higher octane value.

One of the principal objects of the invention is to provide a process for reforming naphthene containing hydrocarbon distillates boiling approximately in the gasoline range to produce high yields of gasoline of desired enhanced octane quality and of good lead susceptibility while minimizing the occurrence or extent-of other accompanying reactions, such as cracking, which tend to produce coke and low molecular Weight hydrocarbon gases, at the expense of desired gasoline yields, while maintaining high catalyst activity.

When employing reforming catalysts of the noble metal-alumina type in the reforming of hydrocarbon dis tillates boiling in the gasoline range, a gradual decline of catalyst activity is observed under operating conditions severe enough to give an octane level of at least 85 F1. clear in the reformed hydrocarbons. The decline in catalyst activity has been attributed to catalyst poisoning as with by-products formed in side reactions occurring at such operating conditions and to the formation of coke deposits on the catalyst. Thus, while reforming does take place under such conditions, other simultaneous reactions occur to substantial extent, including cracking of parts of the charge with the formation of significant quantities of low molecular weight hydrocarbon gases, and may include deposition of coke in sufiicient amounts to limit the practical on-stream operating period of the catalyst.

In accordance with the present invention, the feed stock is first fractionated into a lower boiling fraction and a higher boiling fraction. The lower boiling fraction is then charged to a suitable catalytic reforming unit at relatively severe conditions permitting dehydrogenation, dehydroisomerization and isomerization of the hydrocarbons with resultant good conversion to aromatics and other compounds of desirably high octane values.

The higher boiling fraction is treated with a reforming catalyst under relatively milder conditions. This higher boiling fraction does not require extensive isomerization and primarily requires dehydrogenation which is a relatively fast reaction. The higher boiling fraction is, however, less refractory than the lower boiling fraction and is, therefore, more susceptible to cracking and the forma tion of undesirable by-products which decrease catalyst activity. Accordingly, the present process enables the reforming of the high boiling fraction under con-diticns which are relatively mild in respect to conditions required in conventional reforming of the base stock and in respect to conditions required for the reforming of the low boiling fractions.

In a naphtha charge boiling approximately in the range of gasoline (which may be a virgin naphtha or a naphtha derived from thermal cracking or catalytic cracking) the naphthene content will comprise (1) components which can be converted to benzene by dehydrogenation or dehydroisomerization (so-called benzene formers) and (2) higher boiling components which are converted to toluene, xylene, and to lesser extent to higher boiling alkyl aromatics. The cut point which will be selected in dividing the low boiling portion of the total charge from the higher boiling portion thereof will, of course, depend upon the particular naphtha being treated. As a general rule the cut point employed will be such that the lower boiling fraction will contain all of the toluene formers and may contain some of the lower boiling xylene formers. However, most of the xylene formers and higher molecular weight components should always be in the higher boiling fraction. Both dehydrogenation and dehydroisomerization are favored at lower pressure from the standpoint of thermodynamic equilibrium yields, but pressure is a less important factor in the formation of toluene and xylene from the corresponding naphthenes than in the case of forming benzene. However, lower pressures and lower hydrogen partial pressures in the process tend to produce greater quantities of coke, representing not only loss of charge but effecting rapid deactivation of the catalyst. Additionally, the higher boiling compounds tend to produce coke more readily.

Insplitting the charge into two fractions, in accordance with the invention, therefore, the two-fold advantage is obtained in reducing the coking tendencies of the higher boiling fraction by operating at a higher pressure while ermitting the use of the lower pressure where most needed from equilibrium considerations, i. e. in the treatment of the lower boiling fractions.

The conversion of naphthenes to aromatics is in all instances favored by increase in temperature, but this is limited by the relative refractoriness of the components of the charge being treated, since at increasing temperatures there is a greater tendency for the formation of coke. By treating the higher boiling components at the lower temperature, their coking tendency is thereby reduced. The higher temperature i employed with the lower boiling materials having less tendency to coke with all of the needed advantages that the higher temperature contributes to the conversion by dehydrogenation and dehydroisomerization.

Change in space rate operates somewhat in the same manner, in that the lower the space rate (greater severity), the greater is the tendency toward cracking the lower molecular weight gaseous compounds and the concomitant production of coke.

The cut point for naphthas boiling from about 400 F. is preferably in the range of from about 260 to 300 F. The relatively severe conditions under which the lower boiling fraction is reformed preferably comprise pressures of the order of about l50500 p. s. i. g., temperatures of about 9001050 F., space rates of about 0.5 to about 4 and hydrogen to oil mol ratios of about 3:1 to about 10:1.

The relatively milder conditions under which the higher boiling fraction is reformed preferably comprise pressures of the order of about 400-700 p. s. i. g., temperatures of about 800950 F., space rates of about 3 to about 10 and hydrogen to oil mol ratios of about 3:1 to about 10:1. For any given degree of severity or relative mildness, as the case may be, higher temperatures should be compensated by higher space rates and/or higher pressures as is well known in the hydrocarbon reforming art.

Both the relatively severe and the relatively milder reforming operations are preferably performed in the presence of the same type of reforming catalyst, such as a of these lower boiling materials noble metal-alumina catalyst. The preparation of a preferred type of reforming catalyst is set forth in the following example:

Example I Commercial activated alumina pellets (Harshaw) were treated with acetic acid solution for one hour, decanted, and the treatment repeated for another hour with fresh acid of the same concentration, an amount of acid being employed just sufficient to cover the pellets. The treated pellets were then washed a number of times with water, dried at 200 F. and calcined in air at 900 F. As explained in US. Patent 2,723,947, such aceticacid treatment of the activated alumina particles imparts advantageous characteristics tothe alumina so that such particles are superior carriers in a reforming catalyst. The calcined pellets were then dipped for /2 hour in a chloroplatinic acid solution of sufiicient strength to give about 0.6% platinum on the finished catalyst. The impregnated catalyst was then dried at 200 F. and calcined at 1050' F. in air for 2 hours. On analysis the finished catalyst was found to contain 0.5% by weight of platinum.

The platinum-acetic acid treated alumina catalyst preferably contains from about 0.05 to 2% platinum for optimum reforming of naphthas. The preferred concentration is in the range of 0.1 to 0.6% platinum.

Another preferred type of reforming catalyst for use in the present invention comprises platinum on, alumina which has had any cracking activity substantially curtailed or inactivated with a small amount of an alkaline earth metal oxide. The preparation of such a catalyst suitable for use in the present invention is set forth in Example. II.

Example 11 Commercial activated alumina tablets (Harshaw) were treated with about 5 times their volume of a aqueous solution of MgCl passed over the tablets at the rate of about milliliters solution per liter of tablets per minute. The first fifth of the effiuent was discarded and the remainder recycled twice over the tablets. The thus treated tablets were then washed in water until free of chloride ion and dried overnight at 180 F.

An aqueous solution comprising 26.7 grams of chloroplatinic acid (l-l Ptcl per liter was then poured over the dried tablets, employing the stated solution in an amount furnishing 24.8 grams of chloroplatinic acid per kilogram of the tablets. The mixture was let stand for 56 hour and excess liquid drained. The thus wetted tablets were then dried in an oven at 180 F. overnight and subsequently treated in a muffle furnace at 1050 for 2 hours to drive off HCl, followed by an additional 2 hour heat treatment in flowing air at the same temperature.

The catalyst thus prepared contained by weight of total catalyst0.56% MgO and 0.55% Pt (on 105 C. dry basis).

Further types of reforming catalysts suitable for use in the present invention include palladium or other noble metals on alumina on acetic acid treated alumina or on magnesium oxide inactivated alumina.

"T he reforming process of the present invention may be carried out by first fractionating the base stock into its low boiling and high boiling fractions; then charging the lower boiling fraction to one set of catalytic reactors under relatively severe conditions; and charging the higher boiling fraction to a separate set of reactors under relatively milder conditions. The resultant upgraded products may then be blended with the required lighter hydrocarbons from any suitable source to obtain a full boiling range gasoline of improved high octance value.

.Alternatively, the lower boiling fraction is charged to the first of a series of three or more conventional reactors under relatively severe reforming conditions and the higher boiling fraction is charged only to the second or third reactor in the series used .for reforming of the low boiling-fraction where shorter'contact times and less severe conditions obtain. Thus, this modification in effect enables blending of the high and low boiling fractions under reforming conditions in the second and/or third reactors in the series. The product from this modification of the process is a gasoline of high octane value. It has also been found suitable to charge the low boiling fraction to the first one or more of a series of reactors under relatively severe conditions and to treat the high boiling fraction under selected relatively milder conditions in a separate reactor, thereafter treating the respective eflluents in common remaining reactors of the series.

The product from the afore-described reactions are condensed and scrubbed in the conventional manner and the effluent hydrogen may be recycled.

Deactivation of the reforming catalyst may occur after relatively long continuous use and if desired the catalyst may then be regenerated or reactivated by suitable treatment such as by treatment thereof with hot air suitably diluted with flue gas. In a series of reactor operations as afore-described, the catalyst in one or more of the reactors may be subjected to regeneration without interrupting the continuous on-stream use of the remaining reactors.

The following examples set forth preferred embodiments of the present invention and are not to be construed as limiting same.

Example III An East Texas naphtha was reformed under the following conditions and with the following result:

Catalyst: Pt on acetic acid treated alumina, 0.5% Pt Charge:

Example IV charge as set forth in Example 111 fractions having the following A naphtha fraction was fractionated into two properties:

60.27 39.87 low" high boiling boiling These two fractions were then separately reformed in the same reactor unit and with the same catalyst as that set forth in Example III, the charging amounts corresponding to the relative volumes of each fraction. The products were then blended, as below:

Low High Boiling Bolllng O amt conditions:

Yield, C5+vol. percent".-- 84.3 90.2 Overall yleld, Cal-vol. peroe 86.6 Octane F-l clear, combined 89. 3

Example V A naphtha fraction charge as set forth in Example III was reformed with a Pt on MgO inactivated alumina catalyst containing 0.56% MgO and 0.55% Pt under the following conditions:

Run No. Run No.

Operating Gynditions:

Temp, F 950 950 Pressure, p. s. i. g 550 550 H2: oil, rnols 6 6 Yield, G5+v0l. percent 81.8 87.0 Octane F-l clear 89.2 84. 8

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

What is claimed is:

1. A process for reforming a naphthene containing hydrocarbon distillate fraction boiling within the gasoline range to increase the octane value thereof, which comprises fractionating said hydrocarbon distillate at a cut point in the range of 260 to 300 F. into a relatively low boiling fraction and a relatively high boiling fraction, subjecting said low boiling fraction to relatively severe reforming conditions in the presence of hydrogenand a dehydrogenation-promoting reforming catalyst comprising about 0.5% platinum supported on acetic-acid treated activated alumina particles, subjecting said high boiling fraction to relatively milder reforming conditions in the presence of the same kind of reforming catalyst, and blending said reformed fractions to produce a reformed hydrocarbon product of increased octane value and boiling within the gasoline range; said relatively severe reforming conditions including a temperature in the range of about 900-1050 F., a pressure in the range of about 7 150 to 400 pounds per square inch and a space rate of about 0.5 to 4 volumes of hydrocarbon fraction per hour per volume of catalyst and said relatively mild reforming conditions including a temperature in the range of about 800950 F., a pressure in the range of about 400-700 pounds per square inch and a space rate of about 3 to 10 volumes of hydrocarbon fraction per hour per volume of catalyst; said reforming of the high boiling fraction being effected at a pressure substantially above and at a space rate substantially greater than that at whichsaid low boiling fraction is reformed.

2. The method of upgrading naphtha to achieve a significant yield-octane advantage comprising the steps of: distilling such naphtha into a low boiling fraction having a boiling point range from about 188 to about 270 F. and a high boiling fraction having a boiling point range from about 270 to about 368 F.; reforming each fraction separately; maintaining relatively severe conditions comprising a pressure of about 450 p. s. i. g. and a volume hourly space rate of about 2 for reforming the low boiling fraction; maintaining less severe conditions comprising a pressure of about 600 p. s. i. g. and a volume space rate of about 4 for reforming the high boiling fraction; maintaining constant conditions comprising the presence of catalyst particles consisting of about 0.5% platinum supported on acetic-acid treated activated alumina particles, a hydrogen to hydrocarbon ratio of about 6, and a temperature of about 950 F. for reforming each of said fractions; and blending said reformed fractions to produce a reformed hydrocarbon product of increased octane value and boiling Within the gasoline range.

3. A process for reforming naphthene containing distillate to increase the octane value thereof which comprises: fractionating said hydrocarbon distillate into a relatively lower boiling fraction having an end boiling point within the range from 260 to 300 F. and a relatively high boiling fraction having an initial boiling point Within the range from 260 to 300 F.; subjecting each fraction separately to reforming conditions in the presence of reforming catalyst particles consisting essentially of about 0.5% platinum on acetic-acid treated activated alumina particles and several mols of hydrogen per mol of hydrocarbon at an aromatizing temperature; subj'ecting said low boiling fraction to relatively severe reforming conditions comprising a relatively lower space rate Within the range of about 0.5 to about 4 liquid volumes of hydrocarbon fraction per hour per volume of catalyst, and at a relatively lower pressure within the range of about to about 400 lbs. per sq. in.; subjecting said higher boiling fraction to less severe reforming conditions comprising a relatively higher space rate within the range from about 3 to about 10 liquid volumes of hydrocarbon fraction per hour per volume of catalyst and a higher pressure within the range of about 400 to 700 lbs. per sq. in.; and blending said reformed fractions to produce a reformed hydrocarbon product of increased octane value and boiling within the gasoline range.

References Cited in the file of this patent UNITED STATES PATENTS 2,304,183 Layng et al. Dec. 8, 1942 2,320,147 Layng et al. May 25, 1943 2,324,165 Layne et al. July 13, 1943 2,479,110 Haensel Aug. 16, 1949 2,659,692 Haensel et al. Nov. 17, 1953 

1. A PROCESS FOR REFORMING A NAPHTHENE CONTAINING HYDROCARBON DISTILLATE FRACTION BOILING WITHIN THE GASOLINE RANGE TO INCREASE THE OCTANE VALUE THEREOF, WHICH COMPRISES FRACTIONATING SAID HYDROCARBON DISTILLATE AT A CUT POINT IN THE RANGE OF 260 TO 300*F. INTO A RELATIVELY LOW BOILING FRACTION AND A RELATIVELY HIGH BOILING FRACTION, SUBJECTING SAID LOW BOILING FRACTION TO RELATIVELY SEVERE REFORMING CONDITIONS IN THE PRESENCE OF HYDROGEN AND A DEHYDROGENATION-PROMOTING REFORMING CATALYST COMPRISING ABOUT 0.5% PLATINUM SUPPORTED ON ACETIC-ACID TREATED ACTIVATED ALUMINA PARTICLES, SUBJECTING SAID HIGH BOILING FRACTION TO RELATIVELY MILDER REFORMING CONDITIONS IN THE PRESENCE OF THE SAME KIND OF REFOMING CATALYST, AND BLENDING SAID REFORMED FRACTIONS TO PRODUCE A REFORMED HYDROCARBON PRODUCT OF INCREASED OCTANE VALUE AND BOILING WITHIN THE GASOLINE RANGE; SAID RELATIVELY SEVERE REFORMING CONDITIONS INCLUDING A TEMPERATURE IN THE RANGE OF ABOUT 900-1500*F., A PRESSURE IN THE RANGE OF ABOUT 150 TO 400 POUNDS PER SQUARE INCH AND A SPACE RATE OF ABOUT 0.5 TO 4 VOLUMES OF HYDROCARBON FRACTION PER HOUR PER VOLUME OF CATALYST AND SAID RELATIVELY MILD REFORMING CONDITIONS INCLUDING A TEMPERATURE IN THE RANGE OF ABOUT 800-950*F., A PRESSURE IN THE RANGE OF ABOUT 400-700 POUNDS PER SQUARE INCH AND A SPACE RATE OF ABOUT 3 TO 10 VOLUMES OF HYDROCARBON FRACTION PER HOUR PER VOLUME OF CATALYST; SAID REFORMING OF THE HIGH BOILING FRACTION BEING EFFECTED AT A PRESSURE SUBSTANTIALLY ABOVE AND AT A SPACE RATE SUBSTANTIALLY GREATER THAN THAT AT WHICH SAID LOW BOILING FRACTION IS REFORMED. 